1. Field of the Invention
The present invention relates to an ion beam irradiation apparatus for carrying out a process of implanting ions into a substrate by irradiating the substrate with an ion beam, and a method of operating the ion beam irradiation apparatus. The invention also relates to a method of manufacturing semiconductor devices by implanting ion beams into a semiconductor substrate in a manner that the substrate is irradiated with an ion beam, and more particularly to means for suppressing the accumulatively charging (charge-up) in the surface of the substrate when it is irradiated with the ion beam.
2. Description of the Related Art
When manufacturing semiconductor devices by ion implantation, it is important to suppress the charge-up of the substrate surface when it is irradiated with an ion beam. A charge-up suppressing technique has been proposed in the related art. In the proposed technique, plasma generated by a plasma generator is supplied to an upstream region of the substrate. Electrons contained in the plasma are used for neutralizing the positive charge of the substrate produced by the ion beam irradiation. The proposed technique supplies electrons of lower energy to the substrate, when compared with the technique of utilizing primary electrons emitted from a filament or secondary electrons emitted from an object when the object is irradiated with the primary electrons emitted from the filament. Accordingly, the proposed technique has an advantage of reducing the negative charge in the substrate.
A plasma generator of a radio frequency discharge type is known which generates a plasma by ionizing, using radio frequency discharge, a plasma generating gas that is led into a plasma production chamber. This type of plasma generator is advantageous over the plasma generator of the type which uses the filament for the discharge in the following points: a) the plasma has a long lifetime, and b) it is operable at low gas pressure, and hence the vacuum within a process chamber can be maintained while the plasma is being generated.
One of the problems involved in the plasma generator of the radio frequency (RF) discharge type which utilizes radio frequency discharging for the plasma generation, resides in the plasma ignition.
The plasma generator of the RF discharge type usually includes an electrode (capacitively coupling), e.g., an antenna, or a coil (inductively coupling) for introducing a radio frequency wave into a plasma production chamber. Usually, a magnetic field for generating a plasma and maintaining the generated plasma is applied into the plasma production chamber.
In this case, to ignite a plasma, at least one electron must exist within the plasma production chamber. The electron, accelerated by a high RF electric field, hits an atom or a molecule to ionize them. Then, the electrons emitted as a result of the ionization successively ionize other atoms or molecules. Thus, a plasma is suddenly generated at a certain time point, or in other words, a plasma is ignited.
It is generally considered that the first electron is produced in such a way that high-energy particle beams coming from outer space ionize a gas. The number of electrons that high energy particle beams produce by hitting a gas is much smaller than the number of thermions (usually, several mA) emitted by the filament, for example. Accordingly, it is difficult to reliably ignite a plasma by merely introducing an RF wave into the plasma production chamber.
To reliably ignite an RF plasma, the following methods are employed in the related art.
1) A discharge gap is formed in the plasma production chamber. A high voltage is applied across the gap to cause a discharge, and in turn, the discharge generates a great number of electrons.
2) Laser light of high energy density is introduced into the plasma production chamber. A plasma is ignited by thermally ionizing a plasma generating gas using direct laser light.
In method 1) above, at least one discharge gap electrode having an exposed metal part must be provided within the plasma production chamber. Further, a high voltage source for applying a high voltage to the electrode must also be provided. As a result, the device used for method 1) has complex construction which increases its costs.
After the plasma ignition, the discharge gap electrode is exposed to the plasma and sputtered. Then, the sputtered particles (metal particles) reach the substrate. This results in metal contamination of the substrate.
Further, the discharge causes a surge voltage. Accordingly, there is a danger that the surge voltage adversely affects components of the device, such as for example, the control devices of low voltage in an ion beam irradiation apparatus.
Method 2) requires a laser light source and a laser light transmission window for introducing a laser light emitted from the laser light source into the plasma production chamber. Again, like in method 1), the device used for method 2) has complex construction which increases its costs.
In addition, material deposited during the plasma generation accumulatively attaches to the laser light transmission window. If the amount of the deposited material grows to interrupt the laser light, the plasma ignition becomes impossible. In this case, maintenance is frequently carried out to clean the deposited material, which can become cumbersome.
Accordingly, a principal object of the present invention is to provide a method and apparatus which are capable of reliably and simply igniting a plasma without creating problems such as metal contamination, in a plasma generator of the RF discharge type for the substrate charge-up suppression as mentioned above.
According to one aspect of the present invention, there is provided a method of operating an ion beam irradiation apparatus. In the operating method, when a plasma is ignited in the plasma generator, the ion beam travels beside or in the vicinity of the plasma generator, and in this state a voltage, positive with respective to ground, is applied to the plasma production chamber. Further, secondary electrons, which are generated when the ion beam collides with the plasma generating gas which flows out of the plasma production chamber into a path of the ion beam, are led into the plasma production chamber by the positive voltage, and in the plasma production chamber a plasma ignition is triggered with the secondary electrons led into the plasma production chamber.
In the operating method, an amount of secondary electrons, which is high enough to reliably ignite the plasma, may be led into the plasma production chamber. Accordingly, a plasma may be reliably ignited in the plasma production chamber.
The operating method advantageously utilizes the ion beam, which is originally present for the processing of the substrate, for generating secondary electrons and in turn, the plasma ignition. The plasma may be ignited by the utilization of the ion beam and by applying a positive voltage to the plasma production chamber. Accordingly, the plasma ignition operation is very simple, and complicated means are not needed for the plasma ignition. Further, the operating method does not cause the problems of metal contamination, surge voltage generation, or complicated maintenance.
According to another aspect of the invention, there is provided an ion beam irradiation apparatus which is characterized by a DC power source which applies a voltage, positive with respective to ground, to the plasma production chamber, and leads secondary electrons, which are generated when the ion beam collides with the plasma generating gas which flows out of the plasma production chamber into a path of the ion beam, into the plasma production chamber by the positive voltage, and triggers a plasma ignition with the secondary electrons led into the plasma production chamber, in the plasma production chamber.
In the ion beam irradiation apparatus, an amount of secondary electrons, which is high enough to reliably ignite the plasma, may be led into the plasma production chamber. Accordingly, a plasma may reliably be ignited in the plasma production chamber.
The ion beam irradiation apparatus advantageously utilizes the ion beam, which is originally present for the processing of the substrate, for generating secondary electrons and in turn, the plasma ignition. Means additionally used for igniting the plasma are only a DC power source for applying a positive voltage to the plasma production chamber. Accordingly, the plasma igniting operation is very simple, and there is no need of using complicated means for the plasma ignition. Further, the ion beam irradiation apparatus does not cause the problems of metal contamination, surge voltage generation, or complicated maintenance.
According to yet another aspect of the invention, there is provided an ion beam irradiation apparatus which is characterized by a DC power source which is capable of selecting one of the following operations:
a) to apply a voltage, positive with respective to ground, to the plasma production chamber, and to lead secondary electrons, which are generated when the ion beam collides with the plasma generating gas which flows out of the plasma production chamber into a path of the ion beam, into the plasma production chamber by the positive voltage, and to trigger a plasma ignition with the secondary electrons led into the plasma production chamber, in the plasma production chamber, and
b) to apply a voltage, negative with respective to ground, to the plasma production chamber, thereby controlling an amount of electrons emitted from the plasma production chamber.
In the ion beam irradiation apparatus, the DC power source controls not only the plasma igniting operation as mentioned above, but also an amount of electrons emitted from the plasma production chamber after the plasma ignition. By the control of the amount of emitted electrons, the charge-up in the substrate surface is suppressed to be lower, and the charge voltage of the substrate surface maybe further reduced. Moreover, one DC power source may be used for both the plasma ignition control and the emitted electron amount control. Therefore, the construction is simplified and the cost is reduced when comparing with the case where the power sources are used for those controls, respectively.
According to an additional aspect of the invention, there is provided a method of fabricating semiconductor devices by implanting ions into semiconductor substrates by irradiating the substrate with an ion beam. The method uses a plasma generator which generates a plasma by ionizing a plasma generating gas as introduced into a plasma production chamber by a radio frequency discharge, and supplies the generated plasma to an upstream region of the semiconductor substrate, thereby suppressing the charge-up in a surface of the semiconductor substrate caused by ion beam irradiation. In the semiconductor device fabricating method, the following steps are executed:
A) the ion beam is generated in the plasma generator, and in this state a voltage, positive with respective to ground, is applied to the plasma production chamber, and secondary electrons, which are generated when the ion beam collides with the plasma generating gas which flows out of the plasma production chamber into a path of the ion beam, are led into the plasma production chamber by the positive voltage, and within the plasma production chamber a plasma ignition is triggered with the secondary electrons led into the plasma production chamber, and
B) then, in a state that a voltage, negative with respective to ground, is applied to the plasma production chamber, a plasma is emitted out of the plasma production chamber, and led to an upstream region of the semiconductor substrate, whereby an ion beam is irradiated on the semiconductor substrate while suppressing the charge-up in the semiconductor substrate, caused by ion beam irradiation.
Where this method is used, the plasma can reliably be ignited in the plasma generator as described above, and complicated means are not needed for the plasma ignition. Further, the ion beam irradiation apparatus does not cause the problems of metal contamination, surge voltage generation, or complicated maintenance. Metal contamination of the semiconductor substrate is a serious problem in the fabrication of the semiconductor devices. The invention can prevent this problem. Accordingly, the invention improves the performances of the semiconductor device, and the production yield in the stage of manufacturing the semiconductor devices.
Additionally, an amount of electrons emitted from the plasma production chamber can be controlled by applying a negative voltage to the plasma generator when the semiconductor substrate is irradiated with the ion beam. By the electron amount control, the charge-up in the substrate surface is suppressed to be lower, and the charge voltage of the substrate surface may be more reduced. As a result, the dielectric breakdown of the semiconductor device during the ion beam irradiation is prevented to improve the production yield in the fabrication stage of the semiconductor device. Further, the fabrication method may also be applied to the microfabrication of semiconductor devices.